424 Miscellaneous. 



were obtained but a few days before my departure, and owing to 

 circumstances I could not follow the segmentation any further at 

 the time, and then southerly winds and high water cut off my work, 

 so that I was able to get only the latter half of the development of 

 the eggs I had obtained one afternoon from some of the Ophiurids 

 I had in an aquarium. The eggs were laid in the afternoon about 

 four o'clock, and early next morning the larva already had passed 

 the important stages. One interesting thing was noticed in the 

 segmentation so far as observed. The first two blastomeres, before 

 completely separating, were connected at their middle points by a 

 spindle-shaped body, which was finally constricted off, the two 

 blastomeres having widely separated from each other, then 

 gradually came towards the surface, became spherical, and looked 

 very like a polar globule. The blastomeres rounded out, and again 

 approached each other. Each next divided into two, a body similar 

 to the one mentioned above being given off between each pair of 

 blastomeres, which again widely separated from each other, rounded 

 up, and then approached each other again. At this stage I was 

 obliged to leave. Whether what I saw was the result of a patho- 

 logical condition or not I cannot say. The larvae I found in my 

 aquaria the next morning were pyramidal bodies, somewhat flat- 

 tened, drawn-out gastrula-shaped bodies, of which the anterior 

 bluntly-pointed half was transparent, consisting of a single layer of 

 ciliated ectoderm-cells around a cavity in which were branched 

 mesoderm-cells, and of which the posterior broad end with the 

 blastopore was dark, quite opaque, and already had established in it 

 the enterou with its diverticula. The Ophiurid developed entirely 

 in this posterior half of the larva. The anterior transparent half 

 was gradually resorbed, and, so far as observed, no special invagi- 

 nation for the mouth obtained. On the starfish observed I have 

 nothing new to add at present. 



A few words on the phylogeny of the Echinoderms. If we com- 

 pare the origin of the body-cavity and water-vascular system in the 

 different classes we see that in the Holothurians we have one median 

 pouch given off from the enteron, and that it, by division, gives rise 

 to the body-cavity and water-system. In the Echinoids thero is a 

 two-horned pouch given off. In the starfish there are two separate 

 lateral pouches given off', of which the left gives rise anteriorly to 

 the water-system, and the right and the posterior part of the left 

 become the body-cavity. In Ophiurids, so far as known, there are 

 two separate pouches, both of which divide, the anterior part of the 

 left becoming the water-system, the anterior of the right atrophying, 

 and the posterior parts of the right and left becoming the body- 

 cavity. In the Crinoids there are first given off two separate 

 pouches, which become the body-cavity, and then a single one, that 

 becomes the water-system. Assuming that the story of the Ophi- 

 urids and Crinoids is correct, we have here a rising scale, in which 

 the Holothurians occupy the lowest, the starfish the middle, and the 

 Crinoids the highest position. In favour of this there are some 

 anatomical facts. The objections of palaeontology are not very 

 difficult to answer. In assuming the Holothurians as the primitive 

 forms ii is not necessarily implied that the line of development is a 



